unsprung

I am looking for information regarding the mechanics of Amplify/Dampen magic since I could not find anything close to the answer I am looking for by searching here and elsewhere.

Specifically, I know how Amplify and Dampen work versus players and regular mobs(same as positive or negative +damage/heal) and was wondering if the same mechanics apply to elites and raid bosses. The reason I am asking is because if the same mechanics do apply than Amplify and to a lesser extent Dampen Magic are somewhat under-utilized in the raid environment.

For example, against Prince, would Amplify Magic make Shadow Nova hit for 103 extra damage(3 second cast = ~86% of +damage), or are the mechanics modified? If they are unmodified which is what I would assume, then Amplify Magic is fairly powerful at least on tanks on many fights where there is none to a moderate amount of large damage magic attacks. Dampen would be good in the other case of many frequent low damage magic attacks.